Paper 2013/715

Practical Forward-Secure Range and Sort Queries with Update-Oblivious Linked Lists

Erik-Oliver Blass and Travis Mayberry and Guevara Noubir

Abstract

We present RASP, a new protocol for privacy-preserving range search and sort queries on encrypted data in the face of an untrusted data store. RASP has several advantages over existing work. First, RASP strengthens privacy by ensuring forward security: after a query for range $[a,b]$ any new record added to the data store is indistinguishable from random, even if the new record falls within range $[a,b]$. Surprisingly, we are able to accomplish this using only traditional hash and block cipher operations, abstaining from expensive asymmetric cryptography and bilinear pairings. Consequently, RASP is highly practical, even for large database sizes. Additionally, we require only cloud storage and not a computational cloud like related works, which can reduce monetary costs significantly. The main idea of RASP is to build upon a new update-oblivious bucket-based data structure. We allow for data to be added to buckets without leaking into which bucket it has been added. As long as a bucket is not explicitly queried, the data store does not learn anything about bucket contents. Furthermore, no information is leaked about data additions following a query. Besides formally proving RASP's privacy, we also present a practical evaluation of RASP on Amazon Dynamo, demonstrating its real world applicability.